Robotic systems and computer-assisted devices often include robot or movable arms to manipulate instruments for performing a task at a work site and at least one robot or movable arm for supporting an image capturing device which captures images of the work site. When the robot arms are operating within close proximity to each other, there is a possibility that the arms may collide with one another and by so doing, cause damage to the arms. When the robot arms are commonly operated, preventing such collisions may be straightforward. However, when the robot arms are independently operated, collision avoidance may be much more challenging.
A robot arm comprises a plurality of links coupled together by one or more actively controlled joints. In many embodiments, a plurality of actively controlled joints may be provided. The robot arm may also include one or more passive joints, which are not actively controlled, but comply with movement of an actively controlled joint. Such active and passive joints may be revolute or prismatic joints. The configuration of the robot arm may then be determined by the positions of the joints and knowledge of the structure and coupling of the links.
To avoid collisions between robot arms it is useful to have information of the configurations of the arms and information of their respective positions in a common reference frame. With this information, a controller that is controlling the movement of one of the robot arms can take action to avoid a collision with another robot arm.
One action that the controller may take to avoid collisions is to warn an operator who is commanding a robot arm that a collision with another robot arm is imminent. As one example of such a warning system, U.S. 2009/0192524 A1 entitled “Synthetic Representation of a Surgical Robot,” which is incorporated herein by reference, describes a patient side cart upon which a plurality of robot arms is mounted. As another example of such a warning system, U.S. 2009/0326553 entitled “Medical Robotic System Providing an Auxiliary View of Articulatable Instruments Extending out of a Distal End of an Entry Guide,” which is incorporated herein by reference, describes a medical robotic system having a plurality of articulated instruments extending out of an entry guide. As yet another example of such a warning system, U.S. 2009/0234444 A1 entitled “Method and Apparatus for Conducting an Interventional Procedure Involving Heart Valves using a Robot-based X-ray Device,” which is incorporated herein by reference, describes a medical robotic system in which an X-ray source and detector are mounted on opposing ends of a C-arm so that X-ray images of a patient's anatomy can be captured during the performance of a medical procedure using a catheter control robot.
Collision avoidance may also be performed automatically by a controller which is controlling movement of one or more robot arms. As an example of such an automatic collision avoidance system, U.S. Pat. No. 8,004,229 entitled “Software center and highly configurable robotic systems for surgery and other uses,” which is incorporated herein by reference, describes a medical robotic system that is configured to avoid collisions between its robot arms. The robot arms have redundancy so that multiple configurations are possible for each arm to achieve a desired position and orientation of its held instrument. Each controller commands movement of its associated robot arm subject to a secondary constraint that results in eliminating possible arm configurations that would result in a collision with another robot arm.
When a plurality of robot arms is controlled by a plurality of controllers, however, confusion and unintended consequences may result if more than one of the plurality of controllers is attempting to avoid collisions. This problem is exacerbated when there is none or only limited communication of information between the controllers, such as may be the case when the robotic system employs independently operated robot arms. To avoid robot arm collision problems, the independently operated robot arms may be used sequentially, but not concurrently at the work site. However, it may be advantageous to use the robot arms concurrently during the performance of a procedure or task at a work site.